Air conditioning control system

ABSTRACT

A refrigerant control system, particularly useful for air conditioning apparatus, including means for operating the system with a relatively high evaporator pressure during the time the temperature within the cooled space is being reduced to its desired level. While such temperature level is being reduced, a constant pressure expansion device is adjusted to maintain the control point at a lower temperature (and pressure) to effect dehumidification. This system thus provides a higher capacity during pull-down by modifying the response level of an automatic expansion device until pull-down is achieved. Until either a reduced suction line temperature or a reduced ambient temperature (or both) is attained, the setting of the valve is higher than normal thus increasing the capacity required of the compressor for a given superheat level.

United States Patent [191 Newton Jan. 22, 1974 AIR CONDITIONING CONTROL SYSTEM Alwin B. Newton, York, Pa.

[73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

[22] Filed: July 7, 1972 [21] Appl. No.: 269,636

[75] Inventor:

[52] US. Cl. 62/209, 62/227 [51] Int. Cl. F25b 41/00 [58] Field of Search 62/203, 204, 208, 209, 223,

[56] References Cited UNITED STATES PATENTS 2,940,278 6/1960 Thompson 62/227 3,097,502 62/209 7/1963 Klueger CONTROL INVERTER Primary ExaminerMeyer Perlin Attorney, Agent, or Firm-Donald W. Banner et al.

[57] ABSTRACT A refrigerant control system, particularly useful for air conditioning apparatus, including means for operating the system with a relatively high evaporator pressure during the time the temperature within the cooled space is being reduced to its desired level. While such temperature level is being reduced, a constant pressure expansion device is adjusted to maintain the control point at a lower temperature (and pressure) to effect dehumidification. This system thus provides a higher capacity during pull-down by modifying the response level of an automatic expansion device until pull-down is achieved. Until either a reduced suction line temperature or a reduced ambient temperature (or both) is attained, the setting of the valve is higher than normal thus increasing the capacity required of the compressor for a given superheat level.

1 Claim, 1 Drawing Figure PIUENTEIL 3.. 786.650

CONTROL. INVERTER AIR CONDITIONING CONTROL SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION In U.S. Pat. No. 3,260,064 issued to A. B. Newton on July I2, 1966 there is described an air conditioning system including a compressor, a condenser, an expansion device, and an evaporator, all connected in a closed, vapor cycle refrigeration circuit. An important feature described and claimed in the aforementioned patent is the use of means for sensing the superheat of gas leaving the evaporator and means varying the capacity of the compressor operated in response to the amount of superheat to maintain the correct balance between the compressor capacity and the refrigeration load. This system also uses a constant pressure expansion device between the condenser and evaporator to maintain the evaporator pressure at a predetermined value.

In certain automotive air conditioning applications, especially in the larger size vehicles, which are conven tionally furnished with adequately sized evaporator coils, the critical part of the system is in the compressor. At low suction pressures the efficiency of the compressor is materially reduced in that the refrigerant taken in the suction side of the compressor is in a smaller quantity and less work can be performed on the refrigerant. Automotive applications also present a problem with respect to start-up conditions. For example, the temperature of the air in an enclosed vehicle space, if the auto is parked in the sun with the air conditioning off, may reach as high as 180F. During the time which is required to bring this temperature down to the desired level, commonly referred to as pull-down," the system should be operated in such a manner as to bring this temperature 'down as fast as possible to avoid discomfort to the occupants. On the other hand, it is desirable to provide dehumidification of theair being circulated within the vehicle space. v

i In order to satisfy the first objective, i.e., rapid pulldown, the evaporator pressure should be kept relatively high. This allows more refrigerant to be taken into the compressor suction and provides for efficient use of the entire evaporator coil surface ln other words, during pull-down under normal conditions the refrigerant will completely evaporate in the first section of the evaporator coil. Beyond this point, the temperature of the refrigerant vapor rises (is superheated) and then passes to the compressor suction port. With an adequately sized evaporator coil, the pressure can be raised to effectively increase the capacity of the compressor and utilize most of the evaporator coil surface. To satisfy the requirement of dehumidification after pull-down has been completed, the evaporator pressure should then be lowered to a point slightly above the temperature at which coil freeze-up can occur.

It is an important feature of this invention to provide a system in which the balance or control point of the automatic expansion device is adjusted during pull-' down to reduce the evaporator pressure after the desired temperature has been achieved. When the air DESCRIPTION OF THE DRAWINGS The single FIGURE is a schematic or diagrammatic view of an air conditioning system constructed in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION As shown in the FIGURE, the air conditioning system 0 of the present invention includes a'compressor 10, a

condenser 12, an expansion device 14 and an evaporator 16 all connected to provide a closed circuit refrigeration system. Refrigerant compressed by the compressor is delivered to the condenser through line 18. The liquified refrigerant is then passed through line 20 to expansion device 14, which will be discussed in more detail below. After the refrigerant passes through the expansion device from high pressure side to low pressure side, it flows through line 22 to the evaporator 16 which cools the air circulated over it by fan 17. The refrigerant then flows through line 24, commonly referred to as the suction gas line, to the suction connection of compressor 10.

A control unit 25 has sensors 26, 27 and 28 which measure the superheat of gas leaving evaporator 16 and air temperature in the cooled space. These signals are applied to inverter 29 which varies the energy supplied to compressor motor 30 and the capacity of compressor 10. The details of this control system are described in copending application Ser. No. 264686 entitled Refrigeration Control System by T. C. .lednacz et al. on June 20, 1972 so it is believed to be unnecessary to recite the same in this application. Accordingly, the entire description of the operation of the Jednacz et al. control system is incorporated herein by reference.

Expansion device 14 comprises a valve having a casing 31, a valve member 32 adapted to be seated on valve seat 34, inlet 36 and outlet 37. Valve member 32 is connected toa stem 38 which is secured at its opposite end to an actuating diaphragm 40. Spring 42 is seated upon a spring support member 43 and tends to urge the valve member toward a closed position against seat 34. Spring 44 located in the upper'portion of the casing 31 engages the diaphragm and biases the same in a downward position tending to open the valve by urging valve member 32 away from the seat.

As noted above, an important feature of the invention is the provision of means for establishing a control signal indicative of the interior air temperature and using such signal to vary the control point of the expansion device 14. At the upper portion of the casing 31 there is provided a fluid connection, by means of capillary tube 50, to thermal expansion bulb 52. The chamber 56 formed between the casing 31 and diaphragm 40, together with the capillary and bulb, form a closed system.

Bulb 52 may be attached to the suction line 24, which before starting the system may be at a relatively high temperature. As previously noted, in an automotive system this temperature may reach as high as 180F. After pull-down and achievement of full control, suction line 24 and bulb 52 may be at about F. As car temperature controlled by air temperature sensor 28 is achieved, the control unit calls for increasing superheat thus causing minor warming of line 24 and bulb 52 to again raise response temperature of the constant pressure expansion device to prevent evaporator freeze up.

For example, if the bulb S2 reached 70F., then the diaphragm in the expansion device will return to its original position.

it is not necessary to locate the thermal sensing bulb 52 on the suction gas line 24. Other practical locations may be in the return air stream or in the supply air stream off the evaporator coil. Suitable adjustments in the control to compensate for variations in the different locations will be apparent to those skilled in the art.

Assuming that the vehicle is in a condition where the interior space is relatively warm, the bulb 52, which as previously noted may be located in a position to sense suction gas temperature, will be relatively warm. Accordingly, the fluid charge in the bulb and capillary will be at a high pressure, tending to establish a relatively high pressure not only within the bulb itself but also in chamber 56 which is part of the same closed system. This pressure acting against the upper surface of diaphragm 40 will tend to bias the valve member to its open position and establish a control point effecting a relatively high pressure on the downstream side of the valve, and in the evaporator itself. After the system has been operating for a few minutes (and until the pressure in chamber 56 increases), the pressure on the downstream side of the valve will be maintained constant by the pressure acting against the under side of the diaphragm 40. For example, if the load is changed so as to increase the downstream pressure, this pressure will be applied through passage 45 to the under side of the diaphragm 40, tending to close the valve. If the pressure is reduced for some reason, the opposite result occurs. After the system has been operating for a while at the higher evaporator pressure, the bulb temperature will be reduced tending to reduce the pressure in chamber 56 to relieve the pressure on the upper surface of the diaphragm. This will gradually shift control point at lower and lower pressures until such time as the pulldown phase has been completed. At this point, the evaporator pressure will be established at a point slightly above the temperature at which freeze up can occur, but at a low enough temperature to effect the desired dehumidification of air passing through the evaporator coil.

While this invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit. I

What is claimed is:

l. A refrigerant control system for an air conditioning system of the type including a compressor, a condenser, a constant pressure expansion device and an evaporator connected to provide a closed, vapor cycle refrigerant circuit, said control system comprising means for establishing a control signal which is indicative of the air temperature within the cooled space and means for applying said signal to said constant pressure expansion device to vary the control point thereof, and the corresponding evaporator pressure, whereby the evaporator pressure is established at a lower value when the temperature of the cooled space is below some predetermined value; means for sensing the presence of superheat of refrigerant leaving the evaporator coil; means for sensing the temperature of air circulating within the cooled space and means for deriving a signal based on the amount of superheat and said air temperature for varying the speed of said compressor. 

1. A refrigerant control system for an air conditioning system of the type including a compressor, a condenser, a constant pressure expansion device and an evaporator connected to provide a closed, vapor cycle refrigerant circuit, said control system comprising means for establishing a control signal which is indicative of the air temperature within the cooled space and means for applying said signal to said constant pressure expansion device to vary the control point thereof, and the corresponding evaporator pressure, whereby the evaporator pressure is established at a lower value when the temperature of the cooled space is below some predetermined value; means for sensing the presence of superheat of refrigerant leaving the evaporator coil; means for sensing the temperature of air circulating within the cooled space and means for deriving a signal based on the amount of superheat and said air temperature for varying the speed of said compressor. 